8 Apr
2016
8 Apr
'16
11:27 a.m.
I archive all data sheets I run across and I found
this information
on both TI and Fairchild data sheets for the 78H05, LM340 and LM78XX
devices - it is usually under a heading called Application Hints and
for some reason Fairchild have removed these Hints from the sheets
you quote.
In ALL cases the manufacturers caution that putting
voltage to the
output when the input is not powered CAN DAMAGE THE CHIP.
I have the datasheet PDF for the On Semiconductor version, and I have
been unable to find anything of the sort in it.
Whether On was sloppy when writing their documetnation or whether some
manufacturer's devices are safe or whether I just missed something, I
don't know. But, when dealing with a device of unknown provenance, it
does seem clear you're better off not powering the output side if the
input side has a low-impedance path to ground. (Powering the output
with the input disconnected appears to be a completely different thing;
I have trouble imagining a design that would be damaged by that.)
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